Spinal Device and Method

ABSTRACT

An artificial spinal joint, for creating at least a portion of a coupling between a superior vertebra and an inferior vertebra, comprises an anterior joint replacement component sized to extend into an intervertebral disc space between the superior and inferior vertebrae. The anterior joint replacement component includes a left anterior member separated and spaced apart from a right anterior member. The artificial spinal joint further comprises a bridge component coupled at a first end to the anterior joint replacement and sized to extend posteriorly outside the intervertebral disc space. The bridge component includes a left bridge member separated and spaced apart from a right bridge member. The artificial spinal joint further comprises a posterior joint replacement component coupled to a second end of the bridge component. The posterior joint replacement component includes a left posterior member separated and spaced apart from a right posterior member.

CROSS-REFERENCE

This application claims priority from U.S. Provisional PatentApplication Ser. No. 60/534,960 filed on Jan. 9, 2004, entitled“Posterior Lumbar Arthroplasty.” The following applications also claimpriority to the above referenced provisional application and are relatedto the present application. They are incorporated by reference herein.

-   -   U.S. Utility Patent Application Serial No. (Attorney Docket No.        PC1146), filed on Jan. 7, 2005 and entitled “Spinal Arthroplasty        Device and Method;”    -   U.S. Utility Patent Application Serial No. (Attorney Docket No.        P21756), filed on Jan. 7, 2005 and entitled “Split Spinal Device        and Method;”    -   U.S. Utility Patent Application Serial No. (Attorney Docket No.        P21752), filed on Jan. 7, 2005 and entitled “Interconnected        Spinal Device and Method;”    -   U.S. Utility Patent Application Serial No. (Attorney Docket No.        P21745), filed on Jan. 7, 2005 and entitled “Mobile Bearing        Spinal Device and Method;”    -   U.S. Utility Patent Application Serial No. (Attorney Docket No.        P21743), filed on Jan. 7, 2005 and entitled “Support Structure        Device and Method;”    -   U.S. Utility Patent Application Serial No. (Attorney Docket No.        P21765), filed on Jan. 7, 2005 and entitled “Centrally        Articulating Spinal Device and Method;” and    -   U.S. Utility Patent Application Serial No. (Attorney Docket No.        P21751), filed on Jan. 7, 2005 and entitled “Posterior Spinal        Device and Method.”

TECHNICAL FIELD

Embodiments of the invention relate generally to devices and methods foraccomplishing spinal surgery, and more particularly in some embodiments,to spinal arthroplasty devices capable of being placed posteriorallyinto the vertebral disc space. Various implementations of the inventionare envisioned, including use in total spine arthroplasty replacing, viaa posterior approach, both the disc and facet functions of a naturalspinal joint.

BACKGROUND

As is known the art, in the human anatomy, the spine is a generallyflexible column that can take tensile and compressive loads, allowsbending motion and provides a place of attachment for ribs, muscles andligaments. Generally, the spine is divided into three sections: thecervical, the thoracic and the lumbar spine. FIG. 1 illustratesschematically the lumbar spinal 1 and the sacrum regions 3 of a healthy,human spinal column The sections of the spine are made up of individualbones called vertebrae and the vertebrae are separated by intervertebraldiscs which are situated therebetween.

FIG. 2 illustrates a portion of the right side of a lumbar spinal regionwith a healthy intervertebral disc 5 disposed between two adjacentvertebrae 7, 9. In any given joint, the top vertebra may be referred toas the superior vertebra and the bottom one as the inferior vertebra.Each vertebra comprises a generally cylindrical body 7 a, 9 a, which isthe primary area of weight bearing, and three bony processes, e.g., 7 b,7 c, 7 d (two of which are visible in FIG. 2). As shown in FIG. 7A, inwhich all of the processes are visible, processes 7 b, 7 c, 7 d extendoutwardly from vertebrae body 7 at circumferentially spaced locations.The processes, among other functions, provide areas for muscle andligament attachment. Neighboring vertebrae may move relative to eachother via facet components 7 e (FIG. 2), which extend from thecylindrical body of the vertebrae and are adapted to slide one over theother during bending to guide movement of the spine. There are two facetjoints, each defined by upper and lower facet components, associatedwith adjacent vertebra. A healthy intervertebral disc is shown in FIG.3. As shown in FIG. 3, an intervertebral disc has 4 regions: a nucleuspulposus 11, a transition zone 13, an inner annulus fibrosis region 15and an outer annulus fibrosis 17. Generally, the inner annulus fibrosisregion 15 and the outer annulus fibrosis region 17 are made up of layersof a fibrous gristly material firmly attached to the vertebral bodiesabove and below it. The nucleus pulposus 11 is typically more hydratedin nature.

These intervertebral discs function as shock absorbers and as joints.They are designed to absorb the compressive and tensile loads to whichthe spinal column may be subjected while at the same time allowingadjacent vertebral bodies to move relative to each other a limitedamount, particularly during bending (flexure) of the spine. Thus, theintervertebral discs are under constant muscular and/or gravitationalpressure and generally are the first parts of the lumbar spine to showsigns of “wear and tear”.

Facet joint degeneration is also common because the facet joints are inalmost constant motion with the spine. In fact, facet joint degenerationand disc degeneration frequently occur together. Generally, although onemay be the primary problem while the other is a secondary problemresulting from the altered mechanics of the spine, by the time surgicaloptions are considered, both facet joint degeneration and discdegeneration typically have occurred. For example, the altered mechanicsof the facet joints and/or intervertebral disc may cause spinalstenosis, degenerative spondylolisthesis, and degenerative scoliosis.

One surgical procedure for treating these conditions is spinalarthrodesis (i.e., spine fusion), which has been performed bothanteriorally and/or posteriorally. The posterior procedures includein-situ fusion, posterior lateral instrumented fusion, transforaminallumbar interbody fusion (“TLIF”) and posterior lumbar interbody fusion(“PLIF”). Solidly fusing a spinal segment to eliminate any motion atthat level may alleviate the immediate symptoms, but for some patientsmaintaining motion may be advantageous. It is also known to surgicallyreplace a degenerative disc or facet joint with an artificial disc or anartificial facet joint, respectively. However, none of the known devicesor methods provide the advantages of the embodiments of the presentdisclosure.

Accordingly, the foregoing shows there is a need for an improved spinalarthroplasty that avoids the drawbacks and disadvantages of the knownimplants and surgical techniques.

SUMMARY

In one embodiment, an artificial spinal joint creates at least a portionof a coupling between a superior vertebra and an inferior vertebra. Theartificial spinal joint comprises an anterior joint replacementcomponent extending into an intervertebral disc space between thesuperior and inferior vertebrae. The artificial spinal joint furthercomprises a bridge component coupled to the anterior joint replacementand extending posteriorly from the anterior joint replacement beyond theintervertebral disc space and a posterior joint replacement componentcoupled to the bridge, wherein the posterior joint replacement componentincludes a posterior protrusion engaged with a posterior socket.

In a second embodiment, a spinal arthroplasty device for interpositionbetween a superior vertebra and an inferior vertebra comprises a rostralanterior component movably engaged with a caudal anterior component. Thedevice further comprises a rostral posterior socket engaged with acaudal posterior posterior protrusion and configured to limittranslation of the rostral anterior component relative to the caudalanterior component. In this embodiment, the rostral anterior componentis connected to the rostral posterior component.

In a third embodiment, a method of implanting an artificial spinal jointcomprises making a first incision in a patient's back, removing at leasta portion of a spinal disc from an intervertebral space, inserting atleast a portion of the artificial spinal joint through the incision,positioning an anterior joint portion of the artificial spinal joint inthe intervertebral space, and positioning a posterior joint portion ofthe artificial spinal joint outside of the intervertebral space. Thestep of positioning a posterior joint portion includes engaging aposterior protrusion with a posterior socket.

In a fourth embodiment, a modular artificial spinal joint forinterposition between a superior vertebra and an inferior vertebracomprises an anterior joint replacement component extending into anintervertebral disc space between the superior and inferior vertebrae.The modular artificial spinal joint further comprises a bridge componentremovably coupled to the anterior joint replacement and extendingposteriorly from the anterior joint replacement beyond theintervertebral disc space and a posterior joint replacement componentremovably coupled to the bridge, wherein the posterior joint replacementcomponent includes a posterior protrusion engaged with a posteriorsocket.

The embodiments disclosed may be useful for degenerative changes of thelumbar spine, post-traumatic, discogenic, facet pain orspondylolisthesis, and/or to maintain motion in multiple levels of thelumbar spine.

Additional and alternative features, advantages, uses and embodimentsare set forth in or will be apparent from the following description,drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation schematic view of the lumbar spinal and thesacrum regions of a healthy, human spinal column.

FIG. 2 is a detailed perspective view showing a portion of the rightside of the lumbar vertebrae shown in FIG. 1 with a healthy discdisposed between two vertebrae.

FIG. 3 is a top perspective view of the intervertebral disc shown inFIG. 2 illustrating the major portions of the disc.

FIG. 4 is a side exploded elevation view of a portion of a lumbar spineshowing a first embodiment of an artificial intervertebral jointconstructed according to the principles of the disclosure.

FIG. 5 is an anterior elevation view of a portion of a lumbar spineshowing the superior, disc and inferior portions of the left and righthalves of an assembled artificial intervertebral joint constructedaccording to the first embodiment of the disclosure.

FIG. 6 is a side elevation view of the right half of the artificialintervertebral joint shown in FIG. 5.

FIG. 7A is a transverse, bottom-up-view of a portion of a lumbar spineshowing the superior portion of the artificial intervertebral jointillustrated in FIG. 4.

FIG. 7B is a transverse, top-down-view of a portion of a lumbar spineshowing the inferior portion of the artificial intervertebral jointillustrated in FIG. 4.

FIG. 8 is a transverse, bottom-up-view of a portion of a lumbar spineshowing a second embodiment of a superior portion of an artificialintervertebral joint in which pedicle screws are used to assist inimplantation.

FIG. 9 is a transverse, top-down-view of a portion of a lumbar spineshowing a second embodiment of an inferior portion of an artificialintervertebral joint in which pedicle screws are used to assist inimplantation.

FIG. 10 is a lateral view of a portion of a lumbar spine showing thesuperior portion of the artificial intervertebral joint shown in FIG. 8with one of the pedicle screws being visible.

FIG. 11 is a lateral view of a portion of a lumbar spine showing theinferior and integrated disc portions of an artificial integralintervertebral joint shown in FIG. 9 with one of the pedicle screwsbeing visible.

FIG. 12 is a posterior view of a portion of a lumbar spine showing thesuperior portion of the artificial intervertebral joint shown in FIG. 8with two pedicle screws being visible.

FIG. 13 is a posterior view of a portion of a lumbar spine showing theinferior portion of the artificial intervertebral joint shown in FIG. 9with two pedicle screws being visible.

FIG. 14 is a side elevation view of a portion of a lumbar spine showingthe second embodiment with pedicle screws in an assembled position.

FIG. 15 is a posterior view of a portion of a lumbar spine showing athird embodiment of the inferior, disc and superior portions of anartificial intervertebral joint in which tension bands are used.

FIG. 16 is a side elevation view of a portion of a lumbar spine showingthe third embodiment in which tension bands are used in an assembledposition.

FIG. 17 is a transverse, bottom-up-view of a portion of a lumbar spineshowing the superior portion of a fourth embodiment of an artificialintervertebral joint constructed according to the principles of thedisclosure in which the facet joints are not replaced.

FIG. 18 is a transverse, top-down-view of a portion of a lumbar spineshowing the inferior portion of the fourth embodiment of an artificialintervertebral joint.

FIG. 19 is an exploded perspective view of another embodiment of thepresent disclosure.

FIG. 20 is an assembled side elevation of the embodiment of FIG. 19.

FIG. 21 is an exploded side elevation view of another embodiment of thepresent disclosure.

FIG. 22 is a posterior elevation view of the embodiment of FIG. 21.

FIG. 23 is an exploded perspective view of another embodiment of thepresent disclosure.

FIG. 24 is an assembled perspective view of the embodiment of FIG. 23.

FIG. 25 is an assembled side elevation of another embodiment of thepresent disclosure.

FIG. 26 is an assembled side elevation of another embodiment of thepresent disclosure.

FIG. 27 is an assembled side elevation of another embodiment of thepresent disclosure.

FIG. 28 is an assembled perspective view of another embodiment of thepresent invention.

DESCRIPTION

The drawings illustrate various embodiments of an artificialintervertebral joint for replacing an intervertebral disc or thecombination of an intervertebral disc and at least one correspondingfacet joint. Various embodiments of the artificial intervertebral jointaccording to the principles of the disclosure may be used for treatingany of the problems that lend themselves to joint replacement includingparticularly, for example, degenerative changes of the lumbar spine,post-traumatic, discogenic, facet pain or spondylolisthesis and/or tomaintain motion in multiple levels of the lumbar spine.

FIGS. 4-7 illustrate a first exemplary embodiment of an artificialintervertebral joint. As illustrated in FIGS. 4 and 5, each joint iscomposed of two arthroplasty halves, each of which has a spacer or disc19 and a retaining portion 21. The retaining portion 21 includes a firstretaining portion 21 a and a second retaining portion 21 b. In theexample illustrated in FIG. 4, the first retaining portion 21 a issuperior to (above) the second retaining portion 21 b and the disc 19 issituated therebetween. Although the artificial intervertebral jointaccording to this exemplary embodiment has two halves for each of thefirst retaining portion and the second retaining portion, it should beunderstood that alternative embodiments may be implemented such that theartificial intervertebral joint has a single first retaining member, asingle second retaining member and a single spacer. It should also beunderstood that alternative embodiments may also be carried out witharthroplasties having a first retaining portion, a second retainingportion, and/or a disc which each consist of unequal sized halves ormore than two components.

Further, as illustrated in FIG. 4, the first retaining portion 21 a andthe second retaining portion 21 b are situated between two adjacentvertebrae. More particularly, the first retaining portion may besituated along an inferior surface of the upper of the two adjacentvertebrae and the second retaining portion may be situated above asuperior surface of the lower of the two adjacent vertebrae. However, itshould be understood by one of ordinary skill in the art that the firstretaining portion and second retaining portion are not limited to suchan arrangement, and may be oriented in different positions and/or shapeddifferently than what is illustrated herein.

The surfaces of the retaining portions 21 a, 21 b of the arthroplastythat contact the remaining end plates of the vertebrae may be coatedwith a beaded material or plasma sprayed to promote bony ingrowth and afirm connection therebetween. In particular, the surface to promote boneingrowth may be a cobalt chromium molybdenum alloy with atitanium/calcium/phosphate double coating, a mesh surface, or any othereffective surface finish. Alternatively or in combination, an adhesiveor cement such as polymethylmethacrylate (PMMA) may be used to fix allor a portion of the implants to one or both of the endplates.

As discussed in more detail below, a significant portion of the outerannulus region 17 (see, e.g., FIGS. 4, 7B), in some embodiments about300 degrees, may be retained on the inferior portion of the end plate,which acts as a stop retaining the lower retaining portions in placeuntil bone ingrowth occurs to firmly attach the retaining portions totheir respective vertebrae (FIG. 4 only shows a portion of the outerannulus 17 that is retained). In contrast, in conventional anteriorarthroplasty about 270 degrees of the outer annulus region 17 typicallyis removed. In addition, pedicle screws may also be used for immediatefixation as described in more detail in connection with otherembodiments discussed below.

In the various embodiments of this disclosure, the first retainingportion 21 a and the second retaining portion 21 b are structured so asto retain the disc 19 therebetween. For example, in the case of a disc19 with two convex surfaces 19 a, each of the first retaining portion 21a and the second retaining portion 21 b may have a concave surface 21 cwhich defines a space within which the disc 19 may be retained. Forexample, in the exemplary embodiment shown in FIG. 4, the upper convexsurface 19 a of the disc 19 fits within the concavity defined by theconcave surface 21 c of the first retaining portion 21 a and the lowerconvex surface 19 b of the disc 19 fits within the concavity defined bythe concave surface 21 c of the second retaining portion 21 b.

FIG. 5 illustrates an anterior view of an exemplary assembled artificialintervertebral joint with both arthroplasty halves in place, and FIG. 6shows a side view of the assembled artificial intervertebral joint shownin FIG. 5. As illustrated in FIGS. 5 and 6, the disc 19 is retainedbetween the first retaining portion 21 a and the second retainingportion 21 b. It should be understood that although the disc 19 may beheld between the first retaining portion 21 a and the second retainingportion 21 b, the disc 19 is free to slidably move within the spacedefined by the corresponding surfaces 21 a of the first retainingportion 21 a and the second retaining portion 21 b. In this manner,limited movement between the adjacent vertebrae is provided.

In the exemplary embodiment illustrated in FIGS. 4, 5 and 6, the disc 19is a separate component which is inserted between the first retainingportion 21 a and the second retaining portion 21 b. However, asdiscussed below, it should be understood that the spacer or disc 19 maybe integrally formed with or integrated into in one or both of the firstretaining portion 21 a and the second retaining portion 21 b.

In the exemplary embodiment of the disclosure, as illustrated best inFIGS. 4, 6, 7A and 7B, each of the retaining portions of the artificialintervertebral joint includes a first artificial facet component 23 aand a second artificial facet component 23 b. As shown in FIGS. 7A and7B, the first artificial facet component 23 a has a face 25 a and thecorresponding second artificial facet component 23 b has a face 25 bconfigured such that the face 25 a matingly fits with the face 25 b tostabilize adjacent vertebrae while preserving and guiding the mobilityof each vertebrae with respect to the other vertebrae. Each set of theupper and lower retaining portions 21 a, 21 b may have a pair of facetcomponents 23 a, 23 b, which together define a facet joint. For a totaljoint replacement with facets according to this embodiment, the left andright arthroplasties would define two adjacent facet joints when viewedfrom the posterior.

Regardless of whether artificial facet joints are provided, therespective upper and lower retaining portions associated with the leftand right halves of the arthroplasty may be completely independent fromthe other. That is, as shown in FIG. 7A, for example, the firstretaining portions 21 a associated with each half are not in directcontact with each other. The same is true with respect to the secondretaining portions 21 b shown in FIG. 7B. However, it should beunderstood by one of ordinary skill in the art that, even in theembodiment of the disclosure which includes artificial facet joints, atleast a portion of the first retaining portions 21 a of each half and/orat least a portion of the second retaining portions 21 b of each halfmay directly contact and/or be connected to each other as described inmore detail in connection with the discussion of FIGS. 17-18.

Further, in the various embodiments of the disclosure, the disc 19, thefirst retaining portion 21 a and the second retaining portion 21 b maybe made of any appropriate material which will facilitate a connectionthat transmits compressive and tensile forces while providing for theaforementioned slidable motion in a generally transverse directionbetween each of the adjacent surfaces. For example, in the firstembodiment, the first retaining portion 21 a and the second retainingportion 21 b may be typically made from any metal or metal alloysuitable for surgical implants such as stainless steel, titanium, andcobalt chromium, or composite materials such as carbon fiber, or aplastic material such as polyetheretherketone (PEEK) or any othersuitable materials. The disc may be made from plastic such as highmolecular weight polyethylene or PEEK, or from ceramics, metal, andnatural or synthetic fibers such as, but not limited to, carbon fiber,rubber, or other suitable materials. Generally, to help maintain thesliding characteristic of the surfaces, the surfaces may be polishedand/or coated to provide smooth surfaces. For example, if the surfacesare made of metal, the metal surfaces may be polished metal.

FIGS. 8-14 illustrate a second embodiment of an artificialintervertebral joint. Only features that differ from the firstembodiment are discussed in detail herein. In the second exemplaryembodiment, securing components, such as, for example, pedicle screws 27are provided to provide a more secure and immediate connection betweeneach of the first retaining portion 21 a and/or the second retainingportion 21 b to the corresponding vertebra. In addition, this embodimentillustrates a disc 19 which is integrated with one of the retainingportions, here lower retaining portion 21 b. Disc 19 may be integrallyformed from the same material as its retaining portion, but also may beseparately formed from similar or dissimilar materials and permanentlyconnected thereto to form an integral unit. In this embodiment, the disc19 and the retaining portions may be all formed from metal.

FIGS. 15 and 16 illustrate a third embodiment of an artificialintervertebral joint. In the third exemplary embodiment, additionalsecuring components, such as, for example, tension bands 31 are providedto supplement or replace the function of posterior ligaments that limitthe mobility between adjacent vertebrae by securing the first retainingportion 21 a to the second retaining portion 21 b. As shown in FIGS.15-16, posterior tension bands 31 may be provided by wrapping themaround the corresponding pedicle screws 27 or other convenientattachment points.

FIGS. 17 and 18 illustrate a fourth embodiment of an artificialintervertebral joint. In the exemplary embodiment illustrated in FIGS.17 and 18, the artificial intervertebral joint may have all of thefeatures discussed above except for artificial facet components. In thisembodiment, the natural facet joints remain. The ligamentous tensionband may also be left intact in some embodiments. In addition, thisembodiment includes a specific example of an anterior midline connectionbetween respective upper and lower retaining portions, which assists inmaintaining the placement of the first retaining portion 21 a and thesecond retaining portion 21 b.

FIGS. 17 and 18 illustrate that it is possible to provide a firstretaining portion 21 a with a lock and key type pattern which iscomplemented by the corresponding mating portion provided on the secondretaining portion 21 b. More particularly, one half of the firstretaining portion 21 a has an outer boundary with a U-shaped portion 35a while the other half of the corresponding first retaining portion 21 ahas an outer boundary with a protruding portion 35 b, which fits intothe U-shaped portion 35 a. As a result, each half of the first retainingportion 21 a, 21 b may be maintained in a predetermined position.However, the upper or lower retaining portions may fit together and/orbe connected in the interbody space, e.g., near their midline anteriorportions, in any manner that facilitates implantation and/or assists inproviding and/or retaining the joint in a generally stable, symmetricalconfiguration. It may be even more important to provide such connectionbetween the lower retaining portions due to the inward forces providedby annulus 17 remaining on the inferior end plate as shown in FIG. 18. Amidline connection between the respective lower retaining portions willresist the force of the outer annulus tending to cause migration of theretaining portions toward the midline 37.

As shown in the various exemplary embodiments, other than the portionsof the first and/or second retaining portions which may fit togetherlike a lock and key to maintain the placement of the portions relativeto each other, each half of the artificial intervertebral joint may begenerally symmetrical about the midline 37 of the vertebrae.

Again, these exemplary embodiments are merely illustrative and are notmeant to be an exhaustive list of all possible designs, implementations,modifications, and uses of the invention. Moreover, features describedin connection with one embodiment of the disclosure may be used inconjunction with other embodiments, even if not explicitly stated above.

While it should be readily apparent to a skilled artisan from thediscussion above, a brief description of a suitable surgical procedurethat may be used to implant the artificial joint is provided below.Generally, as discussed above, the artificial intervertebral joint maybe implanted into a body using a posterior transforaminal approachsimilar to the known TLIF or PLIF procedures. According to thisapproach, an incision, such as a midline incision, may be made in thepatient's back and some or all of the affected disc and surroundingtissue may be removed via the foramina. Depending on whether any of thefacet joints are being replaced, the natural facet joints may be trimmedto make room for the artificial facet joints. Then, the halves of theartificial intervertebral joint may be inserted piecewise through theleft and right transforaminal openings, respectively. That is, thepieces of the artificial intervertebral joint including the upper andlower retaining portions, with or without facet components, and theartificial disc, if provided separately, fit through the foramina andare placed in the appropriate intervertebral space. The pieces of theartificial joint may be completely separated or two or more of them maybe tied or packaged together prior to insertion through the foramina bycloth or other materials known in the art. In cases where at least aportion of the outer annulus of the natural disc can be retained, thelower retaining portions of each side of the artificial intervertebraljoint are inserted such that they abut a corresponding portion of theannulus. If a midline anterior connection is provided, the left andright halves of the retaining members are fitted together and held inplace by the outer annulus. As such, the remaining portion of theannulus may be in substantially the same place as it was prior to theprocedure.

Further, in the cases where the annulus of the natural disc must beremoved completely or this is insufficient annulus remaining, it ispossible, for example, to use the embodiment of the disclosure where thepedicle screws are implemented so as to be assured that the pieces ofthe artificial intervertebral joint remain in place. It should beunderstood by one of ordinary skill in the art that the artificial jointcould be implanted via an anterior approach or a combined anterior andposterior approach, although the advantages of a posterior procedurewould be limited. For example, some of the pieces of the artificialintervertebral joint may be inserted from an anterior approach andothers posteriorly. The anteriorly and posteriorly placed portions couldbe fitted together similar to the embodiment shown in FIGS. 17 and 18.

Referring now to FIGS. 19 and 20, in this embodiment, an artificialintervertebral joint 100 may include two arthroplasty halves 102, 104which may be inserted between the vertebrae 7, 9. The arthroplasty half102 may include a rostral anterior joint component 106, a rostralposterior joint component 108, and a rostral bridge 110 extendingbetween the anterior component 106 and the posterior component 108. Thearthroplasty half 102 may further include a caudal anterior jointcomponent 112, a caudal posterior joint component 114, and a caudalbridge 116 extending between the anterior component 112 and theposterior component 114. The rostral anterior joint component 106 mayinclude a bone contacting surface 106 a and the caudal anterior jointcomponent 112 may include a bone contacting surface 112 a. Thearthroplasty half 104 may be substantially similar in structure andfunction to the arthroplasty half 102 and therefore will not bedescribed in further detail.

The terms “rostral” and “caudal” are used in some embodiments todescribe the position of components of the embodiments. While rostral istypically used in the art to describe positions toward the head andcaudal is used to describe positions toward the tail or foot, as usedherein, rostral and caudal are used simply as modifiers for the relativelocations of components of the illustrated embodiments. For example,rostral components may be on one side of an illustrated joint, andcaudal may be on another side of the joint. Components labeled asrostral or caudal to describe an illustrated embodiment are not intendedto limit the orientation of a device or application of a method relativeto a patient's anatomy, or to limit the scope of claims to any device ormethod.

In this embodiment, the rostral bridge 110 may include a jog 117 tocreate an exit portal and an artificial foramen for the exiting nerveroot. Either of the bridges 110, 116, but particularly the caudal bridge116, may be a “super” or artificial pedicle which may supplement orreplace a natural pedicle. Also in this embodiment, the caudal anteriorjoint component 112 may include a curved protrusion 118, and the caudalposterior joint component 114 may include a posterior protrusion 120.The rostral anterior joint component 106 may include an anterior socket122 configured to receive the curved protrusion 118. A radius ofcurvature for the curved protrusion 118 may closely match the radius ofcurvature for the anterior socket 122 to create a highly constrainedball and socket type engagement. In an alternative embodiment, byincreasing the radius of curvature for the socket relative to the radiusof the curved protrusion, the curved protrusion may be permitted totranslate within the socket.

The rostral posterior joint component 108 may include a posterior socket124 configured to engage the posterior protrusion 120. A radius ofcurvature for the posterior protrusion 120 may be smaller than a radiusof curvature for the posterior socket 124, thereby permitting motion andlimiting binding between the posterior joint components 108, 114. Theradii of curvature for the posterior socket 124 and the posteriorprotrusion 120 may emanate from a common center of rotation for thearthroplasty half 102. In this embodiment, the radius of curvature forthe posterior socket 124 is relatively large, and the resulting joint isloosely constrained. In an alternative embodiment, a tight radius ofcurvature for the posterior protrusion of the caudal posterior componentmatched with a rostral posterior component having a tight radius ofcurvature may create a tightly constrained posterior joint.

The size and shape of the anterior components 106, 112 and the bridgecomponents 110, 116 may be limited by the constraints of a posteriorsurgical approach. For example, the anterior components 106, 112 may beconfigured to cover a maximum vertebral endplate area to dissipate loadsand reduce subsidence while still fitting through the posterior surgicalexposure, Kambin's triangle, and other neural elements. To achievemaximum surface coverage, the material of the anterior components 106,112 may extend anteriorly from the curved protrusion 118 and theanterior socket 122, respectively. The width of the bridge components110, 116 are also minimized to pass through Kambin's triangle and toco-exist with the neural elements.

The arthroplasty half 102 further includes features for affixing to thevertebrae 7, 9. It is understood, however, that in an alternativeembodiment, the fixation features may be eliminated. Arthroplasty half102 may include a connection component 130 extending rostrally from therostral anterior joint component 106. The connection component 130 inthis embodiment is an aperture adapted to receive a bone fastener suchas screw 132. The orientation of the connection component 130 permitsthe screw 132 to affix to the cylindrical vertebral body 7 a. In analternative embodiment, the rostral connection component may permitconnection with the pedicle of vertebra 7 as shown, for example, in FIG.14. A few alternative embodiments for the rostral connection componentwill be described below.

Arthroplasty half 102 may further include a connection component 134attached to or integrally formed with the caudal posterior jointcomponent 114. The connection component 134 in this embodiment is anaperture adapted to receive a bone fastener such as screw 136. Theorientation of the connection component 134 permits the screw 136 tobecome inserted extrapedicularly such that the screw travels a pathangled or skewed away from a central axis defined through a pedicle.Extrapedicular fixation may be any fixation into the pedicle that doesnot follow a path down a central axis defined generallyposterior-anterior through the pedicle. In this embodiment, the screwpasses through a lateral wall of the pedicle and may achieve strongcortical fixation. In all embodiments, the screws may be recessed so asnot to interfere with articulations, soft tissues, and neuralstructures.

In an alternative embodiment, for example as shown in FIG. 14, aconnection component extending from the posterior component 114 may beoriented to permit the screw to become inserted intrapedicularly suchthat the screw travels a path generally along the central axis throughthe pedicle. In still another alternative embodiment, the posteriorconnection component may connect to the generally cylindrical bodyportion 9 a. It is understood that in other alternative embodiments, theconnection components may extend at a variety of angles, in a variety ofdirections from the various components of the arthroplasty half. Forexample, a connection component may extend from the rostral bridgerather than the rostral anterior joint component.

As shown in FIGS. 19 and 20, the rostral components 106, 108, 110 of thearthroplasty half 102 are integrally formed. It is understood that in amodular alternative embodiment, these components may be removablycoupled to one another. For example, the rostral anterior jointcomponent may be installed separate from the bridge. After the anteriorcomponent is in place, the bridge may be attached to the anteriorcomponent by any fastening mechanism known in the art, for example athreaded connection, a bolted connection, or a latched connection. Amodular rostral posterior component may then be attached by a similarfastening mechanism to the bridge to complete the rostral portion of thearthroplasty half.

A modular embodiment of the artificial intervertebral joint may beparticularly suited to revision applications in which, for example, theanterior components located between the bodies 7 a, 9 a may be installedin a first surgical procedure and the bridge and/or posterior componentsmay be added in later surgeries to further correct or supplement thefunction of the artificial intervertebral joint. Thus, modular bridgeand/or posterior components may added to a variety of artificialintervertebral joints from a variety of different manufacturers. Forexample, components similar to those described in this disclosure may beused to revise artificial intervertebral joints including thosedescribed in U.S. Pat. No. 6,740,118; and U.S. Patent Application Pub.Nos. 2004/0158328; 2004/0073312; and 2003/0204261, all assigned to SDGIHoldings, Inc. of Wilmington, Del. and incorporated by reference herein;the ProDisc® System described in part by U.S. Pat. No. 5,314,477 andU.S. Patent Application Pub. No. 2004/0117022 (all incorporated byreference herein) and marketed by Spine Solutions, Inc. a subsidiary ofSynthes, Inc. of Oberdorf, Switzerland; or the Charité™ Artificial Discdescribed in part by U.S. Pat. Nos. 4,759,766; 4,997,432; 5,401,269;5,556,431; and 6,416,551 (all incorporated by reference herein) andmarketed by DePuy Spine™, a Johnson & Johnson company. Similarly,modular bridge and/or posterior components may be adapted to be added toany other motion anterior component or to any fusion anterior component.

The arthroplasty halves 102, 104 may be formed of any suitablebiocompatible material including metals such as cobalt-chromium alloys,titanium alloys, nickel titanium alloys, and/or stainless steel alloys.Ceramic materials such as aluminum oxide or alumnia, zirconium oxide orzirconia, compact of particulate diamond, and/or pyrolytic carbon mayalso be suitable. Polymer materials may also be used, including anymember of the polyaryletherketone (PAEK) family such aspolyetheretherketone (PEEK), carbon-reinforced PEEK, orpolyetherketoneketone (PEKK); polysulfone; polyetherimide; polyimide;ultra-high molecular weight polyethylene (UHMWPE); and/or cross-linkedUHMWPE. The various components comprising the arthroplasty halves 102,104 may be formed of different materials thus permitting metal on metal,metal on ceramic, metal on polymer, ceramic on ceramic, ceramic onpolymer, or polymer on polymer constructions.

Bone contacting surfaces of the arthroplasty halves 102, 104 may includefeatures or coatings which enhance the fixation of the implantedprosthesis. For example, the surfaces may be roughened such as bychemical etching, bead-blasting, sanding, grinding, serrating, and/ordiamond-cutting. All or a portion of the bone contacting surfaces of thearthroplasty halves 102, 104 may also be coated with a biocompatible andosteoconductive material such as hydroxyapatite (HA), tricalciumphosphate (TCP), and/or calcium carbonate to promote bone in growth andfixation. Alternatively, osteoinductive coatings, such as proteins fromtransforming growth factor (TGF) beta superfamily, or bone-morphogenicproteins, such as BMP2 or BMP7, may be used. Other suitable features mayinclude spikes, ridges, and/or other surface textures.

The artificial intervertebral joint 100 may be installed between thevertebrae 7, 9 as will be described below. Although installation will bedescribed with respect to arthroplasty half 102, it is understood thatthe arthroplasty half 104 may be installed in a similar mannerGenerally, as discussed above, the artificial intervertebral joint 100may be implanted into a body using a posterior transforaminal approachsimilar to the known TLIF or PLIF procedures. PLIF approaches aregenerally more medial and rely on more retraction of the traversing rootand dura to access the vertebral interspace. The space between thesestructures is known as Kambin's triangle. TLIF approaches are typicallymore oblique, requiring less retraction of the exiting root, and lessepidural bleeding with less retraction of the traversing structures. Itis also possible to access the interspace using a far lateral approach,above the position of the exiting nerve root and outside of Kambin'striangle. In some instances it is possible to access the interspace viathe far lateral without resecting the facets. Furthermore, a directlateral approach through the psoas is known. This approach avoids theposterior neural elements completely. Embodiments of the currentinvention are anticipate that could utilize any of these commonapproaches.

According to at least one of these approaches, an incision, such as amidline incision, may be made in the patient's back and some or all ofthe affected disc and surrounding tissue may be removed via theforamina. The superior endplate surface of the vertebra 9 may be milled,rasped, or otherwise resected to match the profile of the caudalanterior bone contacting surface 112 a, to normalize stressdistributions on the superior endplate surface of the vertebra 9, and/orto provide initial fixation prior to bone ingrowth. The preparation ofthe endplate of vertebra 9 may result in a flattened surface or insurface contours such as pockets, grooves, or other contours that maymatch corresponding features on the bone contacting surface 112 a. Theinferior endplate of the vertebra 7 may be similarly prepared to receivethe rostral anterior joint component 106 to the extent allowed by theexiting nerve root and the dorsal root ganglia. Depending on whether anyof the facet joints are being replaced, the natural facet joints ofvertebrae 7, 9 may be trimmed to make room for the posterior components108, 114.

The halves 102, 104 of the artificial intervertebral joint 100 may thenbe inserted piecewise through the left and right transforaminalopenings, respectively. That is, the pieces of the artificialintervertebral joint 100 including the rostral and caudal anterior jointcomponents 106, 112 respectively fit through the foramina and are placedin the appropriate intervertebral disc space between the generallycylindrical bodies 7 a, 9 a. The pieces of the artificial joint 100 maybe completely separated or two or more of them may be tied or packagedtogether prior to insertion through the foramina by cloth or othermaterials known in the art. In cases where at least a portion of theouter annulus of the natural disc can be retained, the caudal anteriorjoint components of each side of the artificial intervertebral joint areinserted such that they abut a corresponding portion of the annulus. Thebridges 110, 116 may extend posteriorly from the anterior jointcomponents 106, 112 and posteriorly from the intervertebral disc space.The posterior components 108, 114 are positioned posteriorly of theintervertebral disc space to replace or supplement the function of thenatural facet joints. The screw 132 may be inserted through theconnection component 130 and into the generally cylindrical body 7 a,and the screw 136 may be inserted through the connection component 134and into adjacent bone such as the pedicle. It is understood that thescrews may be implanted either after the entire arthroplasty half 102has been implanted or after each of the rostral and caudal component hasbeen implanted.

As installed, the anterior ball and socket type joint created by therostral anterior joint component 106 and the caudal anterior jointcomponent 112 may be relatively stable and self-centering. Both theanterior joint and the posterior joint, created by the rostral posteriorjoint component 108 and the caudal posterior joint component 114, allowthe arthroplasty half 102 to resist shear forces, particularlyanterior-posterior forces. Movement of the rostral anterior jointcomponent 106 relative to the caudal anterior joint component 112 may belimited by the displacement of the posterior protrusion 120 within theposterior socket 124. For example, lateral translation of the rostralanterior joint component 106 relative to the caudal anterior jointcomponent 112 may be limited by the posterior joint. Rotational motionabout a longitudinal axis defined by the cylindrical bodies 7 a, 9 a maybe limited both by the constraint in the posterior joint and by thecombined constraint provided by the two arthroplasty halves 102, 104.Further, the posterior joint may restrict any true lateral bendingdegree of freedom.

Pure freedom of motion may be limited to flexion-extension motion aboutan axis defined through the anterior joints of the arthroplasty halves102, 104. However, under certain conditions, the joint 100 may overcomethese design restrictions to permit limited lateral, rotational, andcoupled movements. For example, the anterior joint components 106, 112may become disconnected or disarticulated from each other and experiencelimited “lift-off,” thereby permitting additional degrees of freedom andcoupled motions beyond strict flexion-extension motion. Theself-centering nature of the anterior joint may encourage reconnectionand alignment after lift-off occurs. The limited disconnection of theanterior joint components 106, 112 may be accommodated by the degree ofconstraint in the posterior joint. For example, relatively looseconstraint in the posterior joint permits greater amounts of lift-off.Some degree of constraint in the posterior joint may be useful, however,to encourage reconnection and alignment of the anterior joint.

In general, a simple, anteriorly located ball and socket joint which istightly constrained with each component having the same or similar radiiof curvature may allow flexion-extension, lateral bending, and torsionmotions while resisting shear forces and limiting translation. By addingan additional highly constrained ball and socket joint to the posteriorcomponents, an additional degree of freedom may be limited, such astorsion. Additional joints may further limit degrees of freedom ofmotion. If the anterior or posterior joints are permitted to disconnector disarticulate additional degrees of freedom may be permitted asdescribed above. Changing the shape of or clearance between the ball andsocket components will also permit additional degrees of motion.

The robust and forgiving structure of the anterior and posterior jointsalso permits misalignment and slight inaccuracy in the placement of thearthroplasty halves 102, 104. For example, the self-aligning ball andsocket structure of the anterior joint components 106, 112 tolerates acertain amount of misalignment between the components. Thus, theinsertion trajectories for the components 106, 112 may be slightlymisaligned. The interaction of the posterior protrusion 120 and theposterior socket 124 may also accommodate parallel misalignment and/oranterior-posterior misalignment between the arthroplasty halves 102,104.

In an alternative embodiment, a single unilateral arthroplasty half maybe installed. This type of intentional lateralization of the anteriorarticulation may create a wedge effect that may be desirable to treatscoliosis or other pathologic conditions that require balancecorrection. In circumstances in which both arthroplasty halves areinstalled, scoliosis and similar pathologic conditions may be remediedby using anterior components of different heights and shapes. In thisway, the articulating joint replacement assembly may act as a wedge,creating a different intervertebral height than the support jointreplacement assembly.

Referring now to FIGS. 21 and 22, in this embodiment, an artificialintervertebral joint 200 may include two arthroplasty halves 202, 204which may be inserted between the vertebrae 7, 9. The arthroplasty half202 may include a rostral anterior joint component 206, a rostralposterior joint component 208, and a rostral bridge 210 extendingbetween the anterior component 206 and the posterior component 208. Thearthroplasty half 202 may further include a caudal anterior jointcomponent 212, a caudal posterior joint component 214, and a caudalbridge 216 extending between the anterior component 212 and theposterior component 214. The rostral anterior joint component 206 mayinclude a bone contacting surface 206 a and the caudal anterior jointcomponent 212 may include a bone contacting surface 212 a. Thearthroplasty half 204 may be substantially similar in structure andfunction to the arthroplasty half 202 and therefore will not bedescribed in further detail.

In this embodiment, the rostral bridge 210 may include a jog 217 tocreate an exit portal and an artificial foramen for the exiting nerveroot. Also in this embodiment, the caudal anterior joint component 212may include a curved protrusion 218, and the caudal posterior jointcomponent 214 may include a posterior protrusion 220. The rostralanterior joint component 206 may include an anterior socket 222configured to receive the curved protrusion 218. A radius of curvaturefor the curved protrusion 218 may closely match the radius of curvaturefor the anterior socket 222 to create a highly constrained ball andsocket type engagement. In an alternative embodiment, by increasing theradius of curvature for the socket relative to the radius of the curvedprotrusion, the curved protrusion may be permitted to translate withinthe socket.

The rostral posterior joint component 208 may include a posterior socket224 configured to engage the posterior protrusion 220. A radius ofcurvature for the posterior protrusion 220 may be smaller than a radiusof curvature for the posterior socket 224, thereby permitting motion andlimiting binding between the posterior joint components 208, 214. Theradii of curvature for the posterior socket 224 and the posteriorprotrusion 220 may emanate from a common center of rotation for thearthroplasty half 202. In this embodiment, the radius of curvature forthe posterior socket 224 is relatively large, and the resulting joint isloosely constrained. In an alternative embodiment, a tight radius ofcurvature for the posterior protrusion of the caudal posterior componentmatched with a rostral posterior component having a tight radius ofcurvature may create a tightly constrained posterior joint.

The size and shape of the anterior components 206, 212 and the bridgecomponents 210, 216 may be limited by the constraints of a posteriorsurgical approach. For example, the anterior components 206, 212 may beconfigured to cover a maximum vertebral endplate area to dissipate loadsand reduce subsidence while still fitting through the posterior surgicalexposure, Kambin's triangle, and other neural elements. To achievemaximum surface coverage, the material of the anterior components 206,212 may extend anteriorly from the curved protrusion 218 and theanterior socket 222. The width of the bridge components 210, 216 arealso minimized to pass through Kambin's triangle and to co-exist withthe neural elements.

In this embodiment, connection components are omitted. However, it isunderstood that in an alternative embodiment, connection componentssubstantially similar to those described above may be used.

As shown in FIGS. 21 and 22, the rostral components 206, 208, 210 of thearthroplasty half 202 are integrally formed. It is understood that in amodular alternative embodiment, these components may be removablycoupled to one another. For example, the rostral anterior jointcomponent may be installed separate from the bridge. After the anteriorcomponent is in place, the bridge may be attached to the anteriorcomponent by any fastening mechanism known in the art, for example athreaded connection, a bolted connection, or a latched connection. Amodular rostral posterior component may then be attached by a similarfastening mechanism to the bridge to complete the rostral portion of thearthroplasty half.

The arthroplasty halves 202, 204 may be formed of any suitablebiocompatible material including the metals, ceramics, or polymersdescribed above. Futher, any of the bone contacting surfaces of thearthroplasty halves 202, 204 may be treated with the coatings orfeatures described above.

The artificial intervertebral joint 200 may be installed between thevertebrae 7, 9 as will be described below. Although installation will bedescribed with respect to arthroplasty half 202, it is understood thatthe arthroplasty half 204 may be installed in a similar manner.Generally, as discussed above, the artificial intervertebral joint 200may be implanted into a body using a posterior transforaminal approachsimilar to the known TLIF or PLIF procedures. PLIF approaches aregenerally more medial and rely on more retraction of the traversing rootand dura to access the vertebral interspace. The space between thesestructures is known as Kambin's triangle. TLIF approaches are typicallymore oblique, requiring less retraction of the exiting root, and lessepidural bleeding with less retraction of the traversing structures. Itis also possible to access the interspace using a far lateral approach,above the position of the exiting nerve root and outside of Kambin'striangle. In some instances it is possible to access the interspace viathe far lateral without resecting the facets. Furthermore, a directlateral approach through the psoas is known. This approach avoids theposterior neural elements completely. Embodiments of the currentinvention are anticipate that could utilize any of these commonapproaches.

According to at least one of these approaches, an incision, such as amidline incision, may be made in the patient's back and some or all ofthe affected disc and surrounding tissue may be removed via theforamina. The superior endplate surface of the vertebra 9 may be milled,rasped, or otherwise resected to match the profile of the caudalanterior bone contacting surface 212 a, to normalize stressdistributions on the superior endplate surface of the vertebra 9, and/orto provide initial fixation prior to bone ingrowth. The preparation ofthe endplate of vertebra 9 may result in a flattened surface or insurface contours such as pockets, grooves, or other contours that maymatch corresponding features on the bone contacting surface 212 a. Theinferior endplate of the vertebra 7 may be similarly prepared to receivethe rostral anterior joint component 206 to the extent allowed by theexiting nerve root and the dorsal root ganglia. Depending on whether anyof the facet joints are being replaced, the natural facet joints ofvertebrae 7, 9 may be trimmed to make room for the posterior components208, 214.

The halves 202, 204 of the artificial intervertebral joint 200 may thenbe inserted piecewise through the left and right transforaminalopenings, respectively. That is, the pieces of the artificialintervertebral joint 200 including the rostral and caudal anterior jointcomponents 206, 212 respectively fit through the foramina and are placedin the appropriate intervertebral disc space between the generallycylindrical bodies 7 a, 9 a. The pieces of the artificial joint 200 maybe completely separated or two or more of them may be tied or packagedtogether prior to insertion through the foramina by cloth or othermaterials known in the art. In cases where at least a portion of theouter annulus of the natural disc can be retained, the caudal anteriorjoint components of each side of the artificial intervertebral joint areinserted such that they abut a corresponding portion of the annulus. Thebridges 210, 216 may extend posteriorly from the anterior jointcomponents 206, 212 and posteriorly from the intervertebral disc space.The posterior components 208, 214 are positioned posteriorly of theintervertebral disc space to replace or supplement the function of thenatural facet joints.

As installed, the anterior ball and socket type joint created by therostral anterior joint component 206 and the caudal anterior jointcomponent 212 may be relatively stable and self-centering. Both theanterior joint and the posterior joint, created by the rostral posteriorjoint component 208 and the caudal posterior joint component 214, allowthe arthroplasty half 202 to resist shear forces, particularlyanterior-posterior forces. Movement of the rostral anterior jointcomponent 206 relative to the caudal anterior joint component 212 may belimited by the displacement of the posterior protrusion 220 within theposterior socket 224. For example, lateral translation of the rostralanterior joint component 206 relative to the caudal anterior jointcomponent 212 may be limited by the posterior joint. Rotational motionabout a longitudinal axis defined by the cylindrical bodies 7 a, 9 a maybe limited both by the constraint in the posterior joint and by thecombined constraint provided by the two arthroplasty halves 202, 204.Further, the posterior joint may restrict any true lateral bendingdegree of freedom.

Pure freedom of motion may be limited to flexion-extension motion aboutan axis defined through the anterior joints of the arthroplasty halves202, 204. However, under certain conditions, the joint 100 may overcomethese design restrictions to permit limited lateral, rotational, andcoupled movements. For example, the anterior joint components 206, 212may become disconnected from each other and experience limited“lift-off,” thereby permitting additional degrees of freedom and coupledmotions beyond strict flexion-extension motion. The self-centeringnature of the anterior joint may encourage reconnection and alignmentafter lift-off occurs. The limited disconnection of the anterior jointcomponents 206, 212 may be accommodated by the degree of constraint inthe posterior joint. For example, relatively loose constraint in theposterior joint permits greater amounts of lift-off. Some degree ofconstraint in the posterior joint may be useful, however, to encouragereconnection and alignment of the anterior joint.

The robust and forgiving structure of the anterior and posterior jointsalso permits misalignment and slight inaccuracy in the placement of thearthroplasty halves 202, 204. For example, the self-aligning ball andsocket structure of the anterior joint components 206, 212 tolerates acertain amount of misalignment between the components. Thus, theinsertion trajectories for the components 206, 212 may be slightlymisaligned. The interaction of the posterior protrusion 220 and theposterior socket 224 may also accommodate parallel misalignment and/oranterior-posterior misalignment between the arthroplasty halves 202,204.

Referring now to FIGS. 23 and 24, in another embodiment, an artificialintervertebral joint may include an arthroplasty half 302 which may beinserted between the vertebrae 7, 9 on one lateral side. A secondarthroplasty half (not shown) may be inserted on the opposite lateralside and may have a similar configuration and function. The arthroplastyhalf 302 may include a rostral anterior joint component 306, a rostralposterior joint component 308, and a rostral bridge 310 extendingbetween the anterior component 306 and the posterior component 308. Thearthroplasty half 302 may further include a caudal anterior jointcomponent 312, a caudal posterior joint component 314, and a caudalbridge 316 extending between the anterior component 312 and theposterior component 314.

In this embodiment, the caudal anterior joint component 312 may includea curved protrusion 318, and the caudal posterior joint component 314may include a posterior protrusion 320. The rostral anterior jointcomponent 306 may include an anterior socket 322 configured to receivethe curved protrusion 318. The rostral posterior joint component 308 mayinclude a posterior socket 324 shaped like a trough and configured toengage the posterior protrusion 320 such that the surface 320 ispermitted to ride in the trough.

In this embodiment, a keel 321 may extend from the caudal anterior jointcomponent 312 and along the caudal bridge 316. The keel 321 may allowthe arthroplasty half 302 to engage the superior endplate of thevertebral body 9 a and a superior face of a pedicle of vertebra 9. It isunderstood that the superior endplate of the body 9 a and the pedicle ofvertebra 9 may be milled, chiseled, or otherwise prepared to create achannel for receiving the keel 321. The keels may help to connect to thebone and limit movement of the arthroplasty half 302 to the desireddegrees to freedom. The keels may have an angled or semi-cylindricalcross section. It is understood that more than one keel may be used onany given component.

The arthroplasty half 302 may be constructed of any of the materialsdescribed above for joint 100 Likewise, the bone contacting surfaces ofthe arthroplasty half 302 may be coated as described above for joint100. Installation may also proceed in a manner substantially similar tothat described for joint 100.

Without copying the exact structure of the natural facets, thisembodiment may mimic many of the functions of the natural facet joints.In this embodiment, the arthroplasty half 302 may be largely controlledfrom the posterior, where mechanical advantage may be greatest. Arostral-caudal length 326 of the posterior socket 324 may limit theflexion extension range of motion while the lateral width 328 of theposterior socket may limit the rotational range of motion. For example,as shown in FIG. 23, where the length 326 is greater than the length ofthe posterior protrusion 320, a range of flexion-extension motion ispermitted as the posterior protrusion 320 travels within the posteriorsocket 324. With little or no clearance between the posterior protrusion320 and the width 328 of the posterior socket 324, rotational motion maybe largely eliminated. Both the anterior joint and the posterior jointallow the arthroplasty half 302 to resist shear forces, particularlyanterior-posterior forces.

In this embodiment, the anterior joint formed by the anterior socket 322and the curved protrusion 318 may have a flexion-extension axis ofrotation 330 positioned posteriorly relative to a midline 332 of thecaudal anterior joint component 312. When installed between thevertebrae 7, 9, the axis 330 may also be positioned posteriorly relativeto the longitudinal axis defined by the generally cylindrical bodies 7a, 9 a, thus placing the center of motion in a more natural position.

Referring now to FIG. 25, in this embodiment, an artificialintervertebral joint 400 may include two arthroplasty halves 402, 404which may be inserted between the vertebrae 7, 9. The joint 400 may besubstantially similar to joint 100 except for the following differences.In this embodiment, the arthroplasty half 402 may include a rostralconnection component 406 which may include a set of spikes or pins. Asthe arthroplasty half 402 is inserted between the vertebrae 7, 9, thespikes advance to engage the cylindrical body portion 7 a.

Referring now to FIG. 26, in this embodiment, an artificialintervertebral joint 420 may include two arthroplasty halves 422, 424which may be inserted between the vertebrae 7, 9. The joint 420 may besubstantially similar to joint 100 except for the following differences.In this embodiment, the arthroplasty half 422 may include a caudalanterior joint component 426, a caudal posterior joint component 428,and a caudal bridge 430 extending between the components 426, 428. Thecaudal posterior joint component 428 may include a motion stop 432. Thearthroplasty half 422 may also include a rostral posterior jointcomponent 434 comprising motion stops 436, 438.

The posterior joint formed by components 428, 434 may be assembled suchthat motion stop 432 is positioned between motion stops 436, 438. Underanterior-posterior shear loads, displacement may be limited or preventedby the interaction of motion stop 436 against motion stop 432.Flexion-extension motion may be limited by the distance between thestops 436, 438, which act as motion limits for the motion stop 432.

The arthroplasty half 422 may further comprise a caudal connectioncomponent 440 extending from the caudal bridge 430. In this embodiment,the connection component 440 is angled such that a bone screw placedthrough the connection component engages the generally cylindrical bodyportion 9 a.

Referring now to FIG. 27, in this embodiment an artificialintervertebral joint 450 may include two arthroplasty halves 452, 454which may be inserted between the vertebrae 7, 9. The joint 450 may besubstantially similar to joint 100 except for the following differences.In this embodiment, the arthroplasty half 452 may include a caudalconnection component 456 which may include an aperture angled such thata bone screw inserted through the aperture engages the generallycylindrical body portion 9 a.

Referring now to FIG. 28, in this embodiment, one arthroplasty half 502of an artificial intervertebral joint may be inserted between thevertebrae 7, 9. It is understood that a second arthroplasty half (notshown) may be inserted on an opposite lateral side, similar to theembodiments described above. The arthroplasty half 502 may include arostral anterior joint component 506, a rostral posterior jointcomponent 508, and a rostral bridge 510 extending between the anteriorcomponent 506 and the posterior component 508. The arthroplasty half 502may further include a caudal anterior joint component 512, a caudalposterior joint component 514, and a caudal bridge 516 extending betweenthe anterior component 512 and the posterior component 514. The rostralanterior joint component 506 may include a bone contacting surface 506 aand the caudal anterior joint component 512 may include a bonecontacting surface 512 a.

Also in this embodiment, the caudal anterior joint component 512 mayinclude a curved protrusion 518, and the caudal posterior jointcomponent 514 may include a posterior socket 520. The rostral anteriorjoint component 506 may include an anterior socket 522 configured toreceive the curved protrusion 518.

The rostral posterior joint component 508 may include a posteriorprotrusion 524 configured to engage the posterior socket 520. In thisembodiment, the posterior protrusion may be a partial sphere that mayrotate or translate within the socket 520, forming a loosely constrainedball and socket style joint.

The arthroplasty half 502 may further include features for affixing tothe vertebrae 7, 9. It is understood, however, that in an alternativeembodiment, the fixation features may be eliminated. Arthroplasty half502 may include a connection component 530 extending rostrally from therostral anterior joint component 506. The connection component 530 inthis embodiment is a tab with an aperture adapted to receive a bonefastener such as screw 532. The orientation of the connection component530 permits the screw 132 to affix to the cylindrical vertebral body 7a. In an alternative embodiment, the rostral connection component maypermit connection with the pedicle of vertebra 7 as shown, for example,in FIG. 14. Arthroplasty half 502 may further include a connectioncomponent 534 attached to or integrally formed with the caudal anteriorjoint component 512. The connection component 534 in this embodiment isa tab with an aperture adapted to receive a bone fastener such as screw536. The orientation of the connection component 534 permits the screw536 to affix to the cylindrical vertebral body 9 a. The connectioncomponents 530, 534 may also function as support tabs, providingadditional surface area to dissipate forces and reduce subsidence.

The arthroplasty half 502 may further include a rostral keel 540extending from the rostral anterior joint component 506 and a caudalkeel 542 extending from the caudal anterior joint component 512 and downthe caudal bridge 516. The keel 540 may allow the arthroplasty half 502to engage the inferior endplate of the vertebral body 7 a, and the keel542 may allow the arthroplasty half 502 to engage the superior endplateof the vertebral body 9 a and a superior face of a pedicle of vertebra9. It is understood that the inferior endplate of the body 7 a may bemilled or otherwise prepared to receive the keel 540 Likewise, thesuperior endplate of the body 9 a and the pedicle of vertebra 9 may bemilled, chiseled, or otherwise prepared to create a channel forreceiving the keel 542. The keels may help to connect to the bone andlimit movement of the arthroplasty half 502 to the desired degrees tofreedom. The keels may have an angled or semi-cylindrical cross section.It is understood that more than one keel may be used on any givencomponent.

The arthroplasty half 502 may be installed similarly to the arthroplastyhalf 102 and may have similar motion in the anterior joint. In thisembodiment, the ball shaped posterior protrusion 524 may be positionedin the socket 520 which is elongated to permit flexion-extension motionwhile limiting torsion. Locating the protrusion 524 on the rostralcomponent 508, may simplify installation as the surgeon's view of thesocket 520 and his/her ability to assemble the posterior joint may beimproved.

Although only a few exemplary embodiments have been described in detailabove, those skilled in the art will readily appreciate that manymodifications are possible in the exemplary embodiments withoutmaterially departing from the novel teachings and advantages of thisdisclosure. Accordingly, all such modifications and alternative areintended to be included within the scope of the invention as defined inthe following claims. Those skilled in the art should also realize thatsuch modifications and equivalent constructions or methods do not departfrom the spirit and scope of the present disclosure, and that they maymake various changes, substitutions, and alterations herein withoutdeparting from the spirit and scope of the present disclosure. It isunderstood that all spatial references, such as “horizontal,”“vertical,” “top,” “upper,” “lower,” “bottom,” “left,” and “right,” arefor illustrative purposes only and can be varied within the scope of thedisclosure. In the claims, means-plus-function clauses are intended tocover the structures described herein as performing the recited functionand not only structural equivalents, but also equivalent structures.

1-61. (canceled)
 62. An artificial spinal joint for creating at least aportion of a coupling between a superior vertebra and an inferiorvertebra comprising: an anterior joint replacement component sized toextend into an intervertebral disc space between the superior andinferior vertebrae, wherein the anterior joint replacement componentincludes a left anterior member separated and spaced apart from a rightanterior member; a bridge component coupled at a first end to theanterior joint replacement and sized to extend posteriorly outside theintervertebral disc space, wherein the bridge component includes a leftbridge member separated and spaced apart from a right bridge member; anda posterior joint replacement component coupled to a second end of thebridge component, wherein the posterior joint replacement componentincludes a left posterior member separated and spaced apart from a rightposterior member.
 63. The artificial spinal joint of claim 62 whereinthe posterior joint replacement component includes a connectioncomponent sized to receive a bone fastener.
 64. The artificial spinaljoint of claim 62 wherein left posterior member and the right posteriormember each include a connection component sized to receive respectivebone fasteners.
 65. The artificial spinal joint of claim 62 wherein thebridge component includes a connection component sized to receive a bonefastener.
 66. The artificial spinal joint of claim 62 wherein the leftbridge member and the right bridge member each include a connectioncomponent sized to receive respective bone fasteners.
 67. The artificialspinal joint of claim 62 wherein the anterior joint replacementcomponent includes a rostral support component sized to abut a posteriorwall of the superior vertebra.
 68. The artificial spinal joint of claim67 wherein the rostral support component includes an aperature sized toreceive a bone fastener.
 69. The artificial spinal joint of claim 62wherein at least one of the left or right anterior members includes ananterior socket in movable engagement with an anterior protrusion.
 70. Amethod of implanting an artificial spinal joint, the method comprising:positioning an anterior joint replacement component within anintervertebral disc space between a superior vertebra and an inferiorvertebra, wherein the anterior joint replacement component includes aleft anterior member separated and spaced apart from a right anteriormember; positioning a bridge component to extend posteriorly outside theintervertebral disc space, the bridge component coupled at a first endto the anterior joint replacement and wherein the bridge componentincludes a left bridge member separated and spaced apart from a rightbridge member; and positioning a posterior joint replacement componentoutside of the intervertebral disc space, the posterior jointreplacement component coupled to a second end of the bridge componentand wherein the posterior joint replacement component includes a leftposterior member separated and spaced apart from a right posteriormember.
 71. The method of implanting an artificial spinal joint of claim70, further comprising fastening the posterior joint replacementcomponent to the inferior vertebra.
 72. The method of implanting anartificial spinal joint of claim 70, further comprising fastening thebridge component to the inferior vertebra.
 73. The method of implantingan artificial spinal joint of claim 70 wherein the step of positioningan anterior joint replacement component includes inserting left andright anterior members through separate openings into the intervertebraldisc space.